The number of surgical procedures performed under assistance from surgical navigation systems has tremendously increased over the last decade. This increase can in part be attributed to the fact that surgical navigation systems have become less complex in use and construction.
Surgical navigation is typically performed on the basis of patient image data (e.g., a Computerized Tomography, or CT, scan) acquired either prior to surgery or intra-operatively. For image-guided surgery the current position of a surgical device relative to the patient is superimposed on the patient image and visualized. The superposition requires registering a navigation reference coordinate system (in which a relative movement between the surgical device and the patient is tracked) with respect to an image coordinate system (in which the patient image data are provided). From a mathematical perspective, the registration involves the calculation of a transformation between the navigation reference coordinate system and the image coordinate system.
After successful registration, the relative movement between a navigated surgical device and the patient can be tracked and visualized. Tracking is performed using a tracking camera configured to detect one or more tracking devices within its field of view. Conventionally, both the patient and the surgical device are each associated with a dedicated tracking device. Such a navigation approach is known, for example, from U.S. Pat. No. 8,457,719 B2 to Stryker Corporation.
U.S. Pat. No. 8,457,719 B2 discloses a tool tracking device and a patient tracking device that each comprise multiple spaced apart tracking points in the form of Light Emitting Diodes, LEDs. The patient tracking device comprises a flexible patch with an adhesive layer on one side to be stuck on to the patient such that the tracking points provided on the opposite side of the patch conform to the patient surface.
The tracking points on the patient tracking device and those on the tool tracking device are detectable by a tracking camera comprised of three separate Charge-Coupled Device (CCD) camera arrays. The tracking camera is mounted to a cart, an operating room wall or an operating room light.
For registration purposes, a model of a patient surface is constructed to which the patient tracking device is stuck on. Construction of the surface model requires localizing the tracking points on the patient tracking device by the tracking camera. In this regard a registration routine instructs the surgeon to move the patient one or multiple times until sufficient tracking points are within the field of view of the tracking camera. As will be appreciated, the quality of the surface model strongly depends on the number of tracking points that can be accurately detected.
Once a reliable surface model has been constructed from the detected tracking points, that surface model is registered to patient image data in the form of a CT scan. The registration can be performed using surface matching techniques. If the scanned patient image and the shape model can be registered within a predetermined error level, the registration routine confirms success of the registration procedure. Success of the registration procedure is strongly influenced by the quality of the surface model. The quality of the surface model, in turn, depends on the number of tracking points accurately detected by the tracking camera.
There also exist navigation approaches in which only the patient is tracked, while the position of the surgical device is calculated relative to the patient tracking device using a priori knowledge about the surgical device and the tracking camera. In this regard, US 2008/0208041 A1 to Activiews Ltd. teaches a surgical navigation system with a patient tracking device in the form of a substantially planar patch that is configured to be applied to a patient. The patch includes an optically detectable tracking point arrangement and an additional radio-opaque fiducial arrangement with a known spatial relationship relative to the tracking point arrangement.
Registration between a pre-operatively taken CT scan and the patient is done by matching the radio-opaque fiducial arrangement identified in the CT scan with the tracking point arrangement detected by a tracking camera attached to the surgical device. During surgical navigation, that device-mounted tracking camera tracks the tracking point arrangement and calculates a position of the surgical device relative to the tracking point arrangement based on knowledge about the geometry of the surgical device, the geometry of the tracking point arrangement and the imaging properties of the tracking camera. As such, there is no need for a separate tool tracking device.